Effects of blood flow restriction and neuromuscular electrical stimulation on muscle hypertrophy in adults: a meta-analysis

Background: Skeletal muscle mass is a key determinant for the preservation of an individual’s health throughout the life span. The application of blood flow restriction (BFR) alone has been shown to attenuate skeletal muscle atrophy in the lower limb following periods of immobilisation. However, it has not been found to provide a sufficient stimulus to promote hypertrophy without the addition of low-load resistance training (20-30% of 1-repetition maximum). Neuromuscular electrical stimulation (NMES) has been used extensively as a rehabilitation technique to attenuate muscle atrophy. The ability of NMES to induce a hypertrophic effect is limited by the application of a high intensity electrical stimulation. It is proposed that the combination of BFR and NMES (C-BFR-NMES) provides a synergistic effect in which hypertrophy may be possible as a passive intervention. The purpose of this systematic review and meta-analysis was to determine the effects C-BFR-NMES compared to BFR or NMES alone or no intervention (CONTROL) on skeletal muscle mass in adults.

Methods: A PRISMA-compliant systematic review and meta-analysis was conducted. The systematic literature research was performed using string terms “blood flow restriction”, “neuromuscular electrical stimulation”, and “hypertrophy” on the following electronic databases from inception to 1 April 2021: PubMed, MEDLINE, Web of Science, Scopus and CINAHL. To determine the standardised mean-difference in skeletal muscle mass change between C-BFR-NMES and CONTROL, a random-effects meta-analysis with inverse variance weighting was conducted.

Results Four comparative studies, including 57 adults, met the eligibility criteria and were included in the meta-analysis. Our results show that C-BFR-NMES compared to CONTROL elicits a significantly greater increase in skeletal muscle mass with a pooled effect size of 0.33 (95% CI 0.10 to 0.57; p=0.01). No studies reported any adverse effects. This systematic review identified varying BFR and NMES protocols and assessment of skeletal muscle mass between studies.

Discussion: This systematic review and meta-analysis suggests that C-BFR-NMES is an effective strategy to stimulate significant skeletal muscle hypertrophy. The practical benefit of C-BFR-NMES extends beyond healthy adults, providing a modality to increase muscle mass for those unable to perform voluntary movement. Future research is needed to further investigate the optimal protocols of C-BFR-NMES to promote skeletal muscle hypertrophy in adults.